Beam centering device for cathoderay tubes



May 20, 1952 P. R. J. COURT 7 BEAM CENTERING DEVICE FOR CATHODE-RAYTUBES Filed Feb. 17, 1950 I nuentor Attorneys Patented May 20, 1952 BEAMCENTERING'DEVICE-FQR CATHODE- RAY TUBES Patrick Richard James Court,Cambridge, Engiassignor t Pye Limite Cambrid e En land, a Briti h panyApplication February 17, 1950, Serial No, 144,688 In Great BritainFebruary'IS, 1949 6 Claims. c1. s s-.45)

The present invention relates to devices for icenteringthe electron beamon the screen of a cathode ray-tube a'nd is particularly applicable tothe centering of the raster on the screen of :thecathode ray tube. of atelevision receiver.

axis thereof.

Each magnet may comprise a single magnet or may'be assembled from a pairof part-annular magnets arranged substantially concentrically to form acomplete annulus but with narrow gaps between the ends of the pair ofmagnets,'like poles" of each of the magnets of a pair lying adjacent oneanother, the two pairs of magnets being disposed side-by-side around theneck of the cathode ray tube and mounted for independent rotation aroundsaid neck and substantially concentrically with the axis thereof.

The'resultant magnetic field due to each annular magnet (or pair ofpart-annular magnets) is very uniform at the centre or axis of the neckof the cathode ray tube where the electron beam passes, and by rotatingeither or both of the Y magnets which are arranged close together butnottouchingaround the tube neck, the strength and direction of theresultant magnetic field along-"the axis of the tube neck may be changedin accordance with the relative positions of the magnets. The magneticfield at the axis of the cathode ray tube will actually be the vectorsum of the two; separate fields.

The magnets maybe conveniently made. quite small, of only slightlylarger internal diameter than theexternal diameter of the neck of thecathode ray tube, and each magnet is preferably thin and fiat in theaxial direction of the assembly. The magnets may be separated from oneanother by an intervening layer of nonmagnetic. material n the'case Whee ch ma t omp is s a pair of part-annular magnets, each part-am nula'r,magnet is preferably almost a complete semi-annulus, so that when a pairof magnets are arranged concentrically only narrow gaps existbetweenadjacent ends of the magnets. The

:maeriasjmay be "carried oninsulating discs or yniembers whichmaybe'cairistructed to rotate aroundthe'neckof the tube, and'the magnets ofonepairmaybe 'separated from the magnets of the other pair by aninterposed layer of -nonmagnetic material.

,The advantages obtained bythe invention are: (1') simplicity, (2)compactness, ('3) economy, (4) a large degree of shift control and (5)ab- .senceof astigmatism, which is due to the fact that the magneticfieldat the centre of each magnet isvery uniform, so that the resultantvector field is very uniform.

. As applied to a. magnetically focussed and magnetically deflectedcathode ray tube, the two magnets may be arranged concentrically roundthe neck of a cathode ray tube, between the focus magnet or con and the,deflector coils. By simply rotating the two magnets with respect to eachother and with respect to the tube, the electron beam may be. moved toany desired position, within the limits imposed by the strength of themagnet fields.

In order that the invention may be more clearly understood referencewill now be made to. the accompanying drawings, in which:

Fig. 1 shows aperspective view of one embodiment according to theinvention.

Fig. 2 shows a view similar to Fig. 1 but with the elements of thecentering device exploded.

Fig. 3 shows a section through the device .mounted on a cathode raytube.

Fig. 4 shows an end view of an alternative construction of magnet.

Referring to Figs. 1, 2 and 3 of the drawings, the centering devicecomprises two annular permanent magnets I, 2 magnetised across theirdiameters as more clearly indicated in Fig. 2. These magnets may be madeof thin sheet metal and are mounted at the front of a focussing thecentre of the assembly. Positioned between the focussing magnet 3 andthe magnet l are three annular spacers of non-magnetic and preferablyinsulating sheet material 5, B and I; between the two magnets I and 2 isa further annulus of non-magnetic sheet material 8; and infrontof themagnet 2 is another annulus of non-magnetic sheet material 9. The wholeassembly is held in position to the front of the focus magnet 3 by meansof three clips [0 secured to the magnet 3 by screws 1 I.

The longitudinally extending limbs l0a of these clips are positioned onecircle correspondingapproximately to the internal diameter of themagnets 1 and 2 so that "the latterare guidingly rotatable therearound.The internal diameters of the spacers are smaller than the internaldiameter of the magnets I and 2, recesses 12 being formed in theinternal peripheries of the spacers to accommodate the clips I0, wherebyrotation of the spacers is prevented. The whole assembly is held againstthe focus magnet 3 by the outwardly turned ends b of the clips 10bearing on the outer surface of the spacer 9. The spacer 6 is of wavy orcorrugated form so as to exert a slight axial pressure on the elementsof the assembly and create friction between the magnets I and 2 and theadjacent spacers so that the magnets will remain in the adjustedposition to which they are turned. To facilitate turning, the magnetsare provided with ears la, 2a extending beyond the external periphery ofthe insulating spacers.

By making the centering assembly narrow in the axial direction, it canbe disposed in between the focus magnet and the deflector coils [4, asshown in Fig. 3.

Centering of the cathode ray beam is achieved by simply rotating the twoannular magnets independently around the neck of the cathode ray tube.

Instead of making each of the magnets I, 2, as a single annular magnetwhich is magnetised across its diameter, each magnet may comprise a pairof flat part-annular magnets 20, 2|, as shown in Fig. 4, fixedconcentrically to a thin flat rin 22 of non-magnetic material. Each ofthe magnets 28, 2| is almost a complete semi-annulus, so that if themagnets are secured concentrically on the supporting ring 22, the endsof the two magnets are spaced apart by narrow gaps. Like poles of thepair of magnets 20, 2| lie adjacent to one another. The central hole 23in each ring 22 is made of a size to fit the neck of the cathode raytube, two such rings each carrying pairs of part-annular magnets beingdisposed around the neck of the tube and arranged sideby-side betweenthe focussing magnet and the deflector coils. The two rings may beseparated by a further ring 25 of non-magnetic material to preventcontact between the two sets of magnets. If desired, two further ringsof non-magnetic material may be used to space the magnet rings from thedeflector coils and from the focus magnet respectively.

The internal peripheries of the magnets 20, 2|, when concentricallysecured on the supporting ring, are preferably slightly spaced from theinternal periphery of the ring, so that the said internal peripheryforms a bearing with the external surface of the neck of the cathode raytube, around which the ring can be rotated. To facilitate adjustment,the rings on which the magnets are mounted may be provided withprojecting arms or lugs.

Whilst particular embodiments have been described, it will be understoodthat various modifications may be made without departing from the scopeof the invention. For example, the

- magnets may be mounted for rotation around the deflection coils. forexample, adjacent the end thereof which lies adjacent the bulb of theoathode ray tube when the deflector coils are mounted on the tube neck.By positioning the beam centering magnets adjacent the bulb of the tube,corner cutting of the beam (that is interception of the deflected beamby the corner of the tube between the neck and bulb portions) may beprevented or reduced. With this embodiment the two magnets may rotatearound a cylindrical member, which may be grooved, fitted around thedeflector coil assembly adjacent one end thereof.

According to a further modification, the pairs of magnets may beprovided with windings, means being provided for varying the currentflowing through the windings. In this way, for example, by arranging thetwo pairs of magnets at right angles to one another, the raster will benormally displaced off-centre and towards one corner of the screen, andby separately energising the windings in opposition to the fieldproduced by the permanent magnets, the position of the raster can beshifted towards the centre. This modification provides a centeringarrangement in which the control is effected electrically instead ofmechanically.

It will also be understood that the arrangement according to theinvention can be applied to cathode ray tubes employing electrostaticdeflection and/ or focussing.

I claim:

1. A device for centering the electron beam of a cathode ray tubecomprising two annular magnets each permanently mag'netised across itsdiameter means for supporting said two magnets side-by-side andcoaxially surrounding the neck of the cathode ray tube, each magnetbeing independently rotatable around the common axis, a thin annularspacer of non-magnetic material positioned between said magnets, andresilient means urging said magnets axially towards one another with thespacer compressed therebetween.

2. A device for centering the electron beam of a cathode ray tubecomprising two annular magnets each permanently magnetised across itsdiameter, each of said magnets being made from thin sheet magneticmaterial with the thickness of the sheet defining the axial length of amagnet, means for supporting said two magnets coaxialiy side-by-side andsurrounding the neck of the cathode ray tube and with each magnetindependently rotatable around the common axis, a thin annular spacer ofnon-magnetic material positioned between said magnets, resilient meansurging said magnets axially towards one another with the spacertherebetween, and means for rotating each of said magnets independentlyabout said common axis.

3. A device for centering the electron beam of a cathode ray tubecomprising a support member having a central aperture through which theneck of a cathode ray tube is adapted to pass, two annular magnets eachpermanently magnetised across its diameter, a plurality of membersextending longitudinally from one side of the support member, the outersurfaces of said members lying on a circle of a diameter correspondingto the internal diameters of the annular magnets and substantiallycoaxial with the aperture in the support member, said annular magnetsbeing arranged side-by-side and surrounding said longitudinal members soas to be independently rotatable therearound, a thin annular spacer ofnon-magnetic material positioned between said annular magnets and havingat least one notch on its inner periphery adapted to engage-- with oneof said longitudinal members to prevent rotation of said spacer, andmeans for holding the two magnets in positions adjacent opposite facesof said spacer respectively.

4. A device as claimed in claim 3, comprising also two annular membersof non-magnetic-material positioned respectively adjacent the-outerfaces of said annular magnets, an annular corrugated member of resilientmaterial positioned between the support member and the annular membernearest thereto, at least one notch in each of said annular members andthe corrugated member engaging with one of the longitudinal members toprevent relative rotation therebetween, abutments carried from the freeends of the longitudinal members and bearing against the end of theouter annular member, said abutments being so spaced from the supportmember that the corrugated member will be slightly compressed andthereby urges the two annular magnets together with the spacertherebetween, and at least one ear projecting from the outer peripheryof each of the annular magnets and beyond the external peripheries ofthe annular members.

5. A combined focussing and beam centering device for the cathode raytube of a television receiver, comprising a focussing device having acentral aperture through which the neck of a cathode ray tube is adaptedto pass, two annular magnets each permanently magnetised across itsdiameter, a plurality of members extending longitudinally from one sideof the focussing device, the outer surfaces of said members lying on acircle of a diameter corresponding to the internal diameters of theannular magnets and substantially coaxial with the aperture in thefocussing device, said annular magnets being arranged side-by-side andsurrounding said longitudinal members so as to be independentlyrotatable therearound, a thin annular spacer of non-magnetic materialpositioned between said annular magnets and having at least one notch onits inner periphery adapted to engage with one of said members toprevent rotation of said spacer, two annular members of non-magneticmaterial positioned respectively adjacent the outer faces of saidannular magnets an annular corrugated member of resilient materialpositioned between the focussing device and the annular member ad-Jacent thereto, at least one notch in each of said annular members andthe corrugated member engaging with one of the longitudinal members toprevent relative rotation therebetween, abutments carried from the freeends of the longitudinal members and bearing against the end of theouter annular member, said corrugated member urging the assembly againstthe abutments, and at least one ear projecting from the outer peripheryof each of the annular magnets and beyond the external peripheries ofthe annular members.

6. A device for centering the electron beam of a cathode ray tubecomprising two annular magnets each permanently magnetised across itsdiameter, means for supporting said two magnets side-by-side andcoaxially surrounding the neck of the cathode ray tube, and with eachmagnet independently rotatable around the common axis, a thin annularspacer of non-magnetic material extending radially between said magnets,and at least one ear connected to and extending outwardly from each ofsaid magnets.

PATRICK RICHARD JAMES COURT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,102,421 Kuehni Dec. 14, 19372,188,579 Schlesinger Jan. 30, 1940 2,195,470 Roosenstein et al. Apr. 2,1940 2,224,933 Schlesinger Dec. 17, 1940 2,455,977 Bocciarelli Dec. 14,1948 2,456,474 Wainwright Dec. 14, 1948 2,498,354 Bocciarelli Feb. 21,1950 2,513,929 Gethman July 4, 1950 2,525,919 Loughren Oct. 17, 19502,544,875 Bennett Mar. 13, 1951 2,544,898 Obszarny et al. Mar. 13, 1951FOREIGN PATENTS Number Country Date 464,637 Great Britain Apr. 21, 1937

